An OLED display apparatus includes a plurality of pixels and a plurality of pixel driving circuits. Each of the pixels corresponds to one of the pixel driving circuit, and is driven by a gate driving circuit and a source driving circuit to display images. The driving circuit includes a driving transistor, a switching transistor, a capacitor, and an organic light emitting diode (OLED). The driving transistor controls a driving current flowing in the OLED. The capacitor uniformly holds a gate voltage of the driving transistor during one frame. The switching transistor stores a data voltage in the capacitor. The current flowing in the OLED relates to a lamination of the pixel. A threshold voltage of the driving transistor is adjustable depending on a process deviation, and electrical characteristics of the driving transistor are degraded based on a driving time. For achieving a desired luminance and increasing life span of the OLED display apparatus, thus a compensation circuit of the pixel driving circuit is needed. Therefore, there is room for improvement in the art.